Plug type circuit breaker



Jhn. 20, 1948. v, A -r 2,434,728

PLUG TYPE CIRCUIT BREAKER Filed Dec. 29, 1945 1 2.9 J 3; 'iw 2 .91

1 '0 INVENTOR.

WUM/XZMS/Mr Patented Jan. 20, 1948 UNITED STATES PATENT OFFICE PLUG TYPE CIRCUIT BREAKER Victor H. Van Sant, Glen Ridge, N. J. Application December 29, 1945, Serial No. 638,058 7 Claims. (Cl. 200-116) This invention relates to an overload circuitbreaker of simple, unique and novel construction, which may be used to replace the ordinary screw type of plug fuse in an electrical circuit.

An object of this invention is to provide a circuit-breaker of the type described, which may be relied upon to open the circuit in which it is placed when the current therein exceeds the value for which the circuit-breaker is designed, and to provide a circuit-breaker which may be manually reset to close the circuit as often as necessary, and which, on each resetting, will again function to open the circuit at the predetermined overload, with accuracy and reliability.

It is a further object to provide a relatively small current-responsive, high resistance element, of very substantial current carrying capacity, which will carry the entire load of the circuit, so that the heat generated within the circuitbreaker will produce an ambient temperature of low magnitude. I

It is a further object to utilize the spring loaded linear expansion of a single metal thermal element of non-oxidizing, high resistant material,

having a, very low creep factor, to performthe function of control within this circuit-breakersuch a metal is a nickel-chrome alloy known by the trade name of Nichrome. This material is widely used in heating elements for electrical appliances, toasters, fiat irons, etc., and may be used continuously at 1150 C. without oxidation. Its linear thermal expansion characteristic from 20 C. (room temperature) up to 600 C. (which will be approximately the maximum operating temperature in this thermal breaker), is 1.32 10- per degree C. Assuming a unit length of three-fourths (A) inch for the thermal element, and a constant normal full load temperature of 500 C., the thermal conducting element in the circuit-breaker will have a linear expansion of 0.0063 inch, and a slight increase beyond this expansion, indicating an overload and in creased temperature, will cause the trip mechanism to function and open the circuit.

It is a further object of this invention to provide a circuit-breaker of such extremely simple compact construction; reliable, accurate operation, and low manufacturing cost, that it may fit into the space ordinarily occupied by a screw plug type of zinc-element fuse, so that it may compete in the market with such a fuse.

Another object of this invention is to provide a circuit-breaker, which may be adjusted externally to trip the circuit open at the desired overload, such adjustment to be made. and the adjustment nut to be permanently soldered, after final assembly of the unit.

It is a further object to provide a circuitbreaker that will have an inherent time lag due to the thermal lag of its functional control element, which is desirable to take care of sudden current surges such as are encountered in the starting of motors, switching on of a bank of incandescent lamps, momentary overloads, etc.

It is a further object to provide a circuitbreaker of the type described, which when open will give a visible indication of that fact, which indication is automatically again obscured when the circuit-breaker is again closed to complete the circuit. An alternate indication not specifically disclosed in the drawings would be a small neon indicating'lamp permanently shunt connected in series with the circuit and housed within the breaker to light up a translucent button when the circuit is open.

While I have shown only a plug type construction of a circuit-breaker employing this unique method of control, it will be apparent to those familiar with the art, that a modification of this same principle of control may be applied in the construction of circuit-breakers to replace ferrule and knife blade types of cartridge fuses.

Other objects of the present invention, not mentioned in the foregoing paragraphs, will become apparent from the following description in connection with the drawings.

The invention is illustrated in the annexed drawings, in which:

Figure 1 is a top end view of the breaker,

Figure 2 is a, sectional elevation on the line 2 Figure 3 is a sectional elevation on the line Figure 4 is a sectional isometric view of th breaker showing the latchin mechanism and the contact bar in open circuit position.

Figure 5 is a diagram showing the contact bar- -ln closed circuit position at its initial setting.

Figure 6 is a diagram showing the circuitbreaker immediately after breaking the circuit.

Figure 7 is an end view of the thermal element adjusting nut.

Figure 8 shows an outline of the keyed opening through the base.

In the various views in which like numerals refer to corresponding parts, the numeral 9 designates a hollow base member of molded insulating material, having on its outer surface one or more male threads I0 provided to screw into the threads 12 of the threaded shell I I. .lrhe threads .3 l2 on this shell are adapted to screw into a standard plug type fuse socket.

The base member 9 has a keyed axial opening i3 in its bottom, into which a threaded stud having a keyway is slidably fitted to receive an adjustment nut l5 by which its lateral position in the base may be accurately located.

on diametrically opposite sides of the base 9 a pair of angular spring contact fingers 26 are located in the recesses 21, their upper bent por tions 28 extend inwardly across the rim of the base to form spring contact surfaces 29, and their lower ends extend down into the base shell II and are soldered thereto at 59, thus serving the doubl purpose of acting as contacts for one side of the circuit and of anchoring the shell H in place. A contact material may be provided on the surface 29 if so desired.

A cap member l8 made of a molded insulating material has a skirt to closely telescope the upper portion of the base 9 and i provided with a partition l9 across it, in position to form, with the interior of the base 9, a substantially closed chamber 29. There is, however, provided in the central hubbed portion of the partition IS, an

axial opening 2| within which there is slidably mounted a push button 22, the upper knurled rim portion 58 of the cap l8 extends to the upper travel limit of the button 22 and acts as a barrier to any external obstruction blocking the complete opening of the circuit-breaker.

A contact bar 39 is attached to the lower end of the button 22 in any convenient manner, as by means of the hollow rivet 3| as shown. This bar extends diametrically across the cap member. l8, each end forming a contacting surface 32 in assembly,-to engage the contacting surfaces 29 on arms 28. Each of these ends i guided in a recess 33 in the sides of the cap l6, and held in alignment with the contacts 28.

The cap 3 i held in assembly with the base 9 by a self tapping, quick-thread-drive stud 56 pressed into the boss 51 in the base cavity, thereby forming a tamper-proof assembly, since it cannot easily be disassembled.

A spring 49, preferably made of beryllium copper or hard Grade A spring tempered Phosphor bronze, is bent back upon itself as shown at 4| to form a fulcrum designed to pivot in a v groove 42 adjacent to, but on one side of, the keyed opening l3. One side of this spring is three-pronged. Of these, the central arm 43 extends up substantially straight and Parallel to the axis of the circuit-breaker, and has its end 45 bent over at right angles. Between this bent over end 44 and the stud N there i streached a wire or ribbon 45 which is spot welded to both members to restrain the spring 49 from swinging about the groove in a counter-clockwise direction.

The two outside arms 46 of these three prongs are bent over as shown in the drawings to bear against the side wall of the chamber 29 at 41 on the other side of the opening l3 to urge the spring 49 in a counter-clockwise direction, and thus, when the parts are assembled, to hold the thermal element 45 taut. Each of these arms continues, as shown at 48, and is bent back beneath the contact'bar 39 in position to bear upwardly against the contact bar in a direction to separate the contacts 29 from the contacts 32 to snap the circuit open. These arms are also provided to carry most of the current from the thermal element to the contact bar 39 in closed circuit position.

The other side 59 of the spring 49 extends upwardly parallel to the arm 49, into a position ad- Jacent to the contact bar 39. On the side of the bar 39 there is an outwardly extending latch lug 5| which, when the button 22 is in closed circuit position, extends through an opening 52 in the latch arm 59. Thus, whenever the button 22 is pushed to circuit closing position it will be held there by the engagement of the latch lug 5| with the side of the opening 52. The upperend of this arm 59 is bent outwardly at an angle as shown at 53 so that, as the button is pushed into circuit closing position, it will bend the arm 59 out of the wayfar enough to permit the latch lug to snap into the opening 52.

A portion of the button 22 is preferably made of a contrasting white or light colored translucent material as shown at 54, while the upper cap portion 55 is made ofthe same dark material as the housing cap |8-the proportions being such that when the circuit is closed no part of the lighter portion of the button will be visible but, when the circuit i open, a white or light colored collar will appear, to indicate the open circuit.

The device may be assembled by first screwing the base shell onto the base 9, placing the two contact fingers 26 in the recesses 21 and soldering them to the base shell to complete the base sub-assembly. Next, the spring 49, with its associated thermal element 45 and keyed anchor stud I4, is placed within the base shell with the stud |4 sliding through the opening l3 and the bend 4| resting in the V-groove 42, the nut I5 is lightly run upon the threads of the stud l4. Button 22 with its associated cross bar 39 is dropped into its position in the cap member l9 and the cap is slid on over the base sub-assembly 9 in proper orientation therewith; the retaining stud 56 is pressed into the boss 51 to complete the assembly.

The button 22 may now be depressed and the nut |5 screwed up until the force of the spring 46 is overcome, and the button is held in its depressed position.

The adjustment of the device to operate at the desired current overload is simple. If, for example, the circuit-breaker is designed to carry thirty (30) amperes at a constant, thermal element, operating temperature of 500 C., a thermal element of high' resistance material, of the proper circular mil cross sectional area and unit length, is chosen to maintain this constant lull load temperature at thirty (30) amperes and has a substantially constant linear expansion over the thermal operating range of the breaker, which will permit the spring 46 to force the latch arm 59 out in a counter-clockwise direction to the end of the latch lug 5|. Additional amperage, through the thermal element, will increase the expansion thereof to permit the latch arm 59 to slip oil the end of the latch lug 5|, and permit the circuit to be snapped open. The nut I5 is adjusted to permit the trip mechanism to 0perate at the desired overload, and is fixed in this position by a drop of solder in the keyway at 69 of the stud l4 to lock the nut in place.

Since the thermal element 45 is actuated by the entire current, and since the expansion or this wire or ribbon 45, in response to the current under given conditions does not fluctuate, the point at which the circuit will open remains fixed at the value for which it is originally set, and can be made to operate within narrow limits. Since, moreover, the expansion of a wire or ribbon, and

its contraction under subsequent cooling, exerts a considerable force, it will be seen that the spring 46 can be made relatively strong with the result that the operation of the circuit-breaker in both directions is quite positive.

Moreover, it will be seen that the pairs of contact on opposite sides of the breaker are in parallel, and that each pair carries substantially onehalf the circuit load, and, therefore, under nor mal conditions are less likely to be burned or pitted in breaking a substantial overload or shortclrcuit. I

An additional consideration is the ability of one pair of contactsto carry the entire load in the event the other pair should become damaged.

Since certain changes may be made in the above construction and different embodiments of the invention could be made without departing from the scope thereof, it is intended that all atter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims areintended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention whichas a matter of language might be said to fall therebetween.

I claim:

1. A circuit-breaker comprising a hollow base having a shell thereon and a coaxial stud slidably extending through the bottom of the base and keyed against rotation, an arm within said base iulcrumed in a V-shaped slot in the bottom of the interior thereof adjacent to the stud, a thermally expansive conducting element stretched between the free end of said arm and said stud, a stationary contact upon said base connected to said shell, a button movable within said base carrying a contact in registry with said stationary contact, spring means for urging said button in a direction to separate said contacts and for urgingsaid arm to move about its pivot in a direction to stretch said conducting element, and a pair of interengaging elements, one carried by said button, and one by said arm, releasable by movement of said arm about its pivot in response to a stretching of said conducting element.

2. A circuit-breaker comprising a hollow base having a shell thereon and a coaxial stud, an arm within said base fulcrumed in a V-shaped slot in the bottom of the interior thereof adjacent to the stud, a thermally expansive conducting element stretched between the free end of said arm and said stud, a stationary contact upon said base connected to said shell, 2. button movable within said base carrying a contact in registry with said stationary contact, spring means for urging said button in a direction'to separate said contacts and for urging saidarm to move about its pivot in a direction to stretch said conducting element, and a pair of interengaging elements, one carried by said button, and one by said arm, releasable by movement of said arm about its pivot in response to a stretching of said conducting element.

3. A circuit-breaker comprising a hollow base having a shell thereon and a coaxial stud, an arm within said base fulcrumed in a V-shaped slot in the bottom of the interior thereof adjacent to the stud, a thermally expansive conducting element stretched between the free end of said arm and said stud, a stationary contact upon said base connected to said shell, a button movable within said base carrying a contact in registry with saidstationary contact, spring means ifor urging said button in a direction to separate ing an inclined surface in the path ofsaid'button adapted to press said spring latch arm out of the way to permit said interengaging members to engage on depression of said. button without stretching said conducting element.

4. A circuit-breaker comprising a hollow base having a shell thereon and a coaxial stud, an

arm within said base fulcrumed in a- V-shaped slot in the bottom of the interior thereof adjacent to the stud, a thermally expansive conducting element stretched between the free end of said arm and said stud, a stationary contact upon said base connected to said shell, a button movable within said base carrying a contact in registry with said stationary contact, spring means for urging said button in a'direction to separate said contacts and for urging said arm to move about its pivot in a direction to stretch said conducting element, and a pair of interenr gaging elements, one carried by said button, and

one by said arm, releasable by movement of said arm about its pivot in response to a stretching of said conducting element, said interengaging element upon said arm being carried by a spring latch arm, said arm and said latch arm being united at the fulcrum, and said spring means comprising extensions of one of said arms bent outwardly and upwardly to engage the side wall of said hollow base and to engage said button.

5. A circuit-breaker comprising a screw type base having a central electrode extending through the bottom thereof, and a shell electrode surrounding the same, a lever within the interior of said base pivoted on the base adjacent to the central electrode, and extending parallel to the axis of the base, a thermally expansible wire connected to said central electrode and to said lever at a point spaced from said electrode, a mechanically movable element within said base, a pair of contacts within said base, one being connected to said shell, and the other being connected to said mechanically movable element in position to engage said first named contact when said element is moved to one position, interengaging members on said lever and element, to hold said element in said one position constructed and arranged to be released when said expansible member expands, and spring means to urge said lever about its ful crum against the tension of said wire and to separate said contacts when released.

6. A circuit-breaker comprising a screw type base having a central electrode extending through the bottom thereof, and a shell electrode surrounding the same, a lever within the interior of said base pivoted on the base adjacent to the central electrode and extending parallel to the axis of the base, a thermally expansible wire connected to said central electrode and to said lever at a point spaced from said electrode, an axially movable button within said base, a pair of contacts within said base, one contact being connected to said shell, and one being connected to said button in position to engage said first named contact when said button is moved to one position, interengaging members on said lever and mamas button to hold said contact connected to said button in said one position, constructed and arranged to be released when said expansible-member expands, and spring means to urge said lever about its fulcrum against the tension of said wire and to separate said contacts when released.

7. A circuit-breaker comprising a screw type base having a central electrode extending through the bottom thereof, and a shell electrode surrounding the same, a lever within the interior of said base pivoted on the base adjacent to the central electrode and extending parallel to the axis of the base, a thermally expansible wire connected to said central electrode and to said lever at a point spaced from said electrode, a mechanically movable element within said base, a pair of contacts within said base, one being connected to said shell, and the other being connected to said mechanically movable element in position to engage said first named contact when said element is moved to one position, interengaging members on said lever and element, to hold said element in said one position constructed and arranged to be released when said expansible member ex 8 pands, and spring means to urge said lever about its fulcrum against the tension of said wire and to separate said contacts when released, said thermally expansible wire being screw connected by said central electrode to said base whereby the tension on said wire may be adjusted to alter the capacity or the circuit-breaker.

VICTOR H. VAN SANT.

10 REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 15 Number Name Date 1,560,597 Meirjohan Nov. 10, 1925 1,627,029 Greenway et a1 May 3, 1927 1,800,710 Weigand Apr. 14, 1931 M FOREIGN PATENTS Number Country Date 96,440 Austria Mar. 26, 1924 443,870 Germany May 12, 1927 

